Where do babies come from?
Babies are created when a man and a woman have sex: the man penetrates the woman's vagina with his penis until ejaculation. Ejaculation is the expulsion of sperm from the penis. Spermatozoa are reproductive cells (male gametes) or in a simplified way human seeds.
If the conditions are right, one or more of the man's sperm meet the woman's ovaries. The ovaries are female gametes (in a simplified way eggs).
When a sperm enters the ovary, they will merge to form the egg cell, this is fertilization. The egg will give an embryo which will gradually transform into a fetus and then take human form in the female body.
After nine months on average, the fetus has become a baby which will be expelled from the mother's body: it is childbirth.